What do the following two equations represent? $3x+3y = 1$ $-9x+9y = 4$
Explanation: Putting the first equation in $y = mx + b$ form gives: $3x+3y = 1$ $3y = -3x+1$ $y = -1x + \dfrac{1}{3}$ Putting the second equation in $y = mx + b$ form gives: $-9x+9y = 4$ $9y = 9x+4$ $y = 1x + \dfrac{4}{9}$ The slopes are negative inverses of each other, so the lines are perpendicular.